Microwave heating devices



K- HILTON ET AL MICROWAVE HEATING DEVICES Oct. 21, 1969 2 Sheets-Sheet 1 Filed Nov. 1, 1967 Oct. 21, 1969 L N ET AL 3,474,213

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United States Patent US. Cl. 2191ii.55 Claims ABSTRACT OF THE DISCLGSURE In a microwave heating device of the kind comprising two complementary parts which together constitute a serpentine slotted waveguide, each of said parts is constructed of rectangular section elongate members with upstanding wall elements interleaved therebetween and end pieces, said elongate members, wall elements being rigidly secured together to constitute a serpertine U-section channel.

This invention relates to a microwave heating device suitable for use in the microwave heating of paper or other sheet material, and more particularly to a waveguide device of the kind described in British Patent Specification No. 1,050,493 and to a particularly advantageous construction of such a device.

In the said specification, there is described and illustrated a waveguide device which comprises two trays, each having disposed within it a series of internal partitions or walls extending from alternate side walls of the tray and stopping short of the other wall so as to define within the tray a serpentine channel, the trays being so related that when one is placed, inverted, over the other they constitute together a waveguide device of which the interior is divided by the internal walls of the two trays into a series of waveguide sections each communicating at its ends, through respective irises, with adjacent sections of the series. The device thus provides a serpentine waveguide, and by arranging that gaps are left between the walls of one tray and the corresponding walls of the other tray the effect is produced that the waveguide sections are slotted sections through which sheet material can be passed in the transverse direction of the waveguide sections through each of them in turn, in a plane which corresponds within the waveguide sections, when they are excited in the H mode, to maximum microwave-frequency voltage and thus provides maximum heating of the sheet material due to its capacity to absorb microwave energy.

It is an object of the present invention to provide a microwave-heating waveguide device of this kind, referred to herein as a microwave heating device of the kind described, and, more particularly, to provide a novel and advantageous construction of such a device.

A preferred embodiment of a microwave heating device according to the invention is shown in the accompanying drawings, in which:

FIGURE 1 shows a general, partly broken away view, of a lower part of the device;

FIGURE 2 shows one of a plurality of similar wall elements comprised by the lower part shown in FIG- URE 1;

FIGURE 3 shows a rear view of a hinge connecting to the lower part of the device, shown in FIGURE 1, a corresponding upper part thereof;

FIGURE 4 shows an end view of the hinge, connecting the said lower and upper parts of the device to one another and part of a waveguide which is secured to the hinge.

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FIGURE 5 shows a waveguide step transformer for connection to a microwave source;

FIGURE 6 shows a waveguide step transformer incorporating a water load; and

FIGURE 7 shows a scrap plan View of the upper part of a device according to the invention and provided with an air inlet manifold and an air exhaust manifold.

The device to which the drawings relate comprises an upper part and a corresponding lower part, the lower part being shown in FIGURE 1.

As shown in FIGURE 1, the lower part comprises a plurality of square-section metal bars 11 having a plurality of sheet metal wall elements 12 interleaved between them and extending about them. As shown in FIG- URE 2, the wall elements 12 are formed each with one cut-away end 13 and one end 14 which is not cut away, and as shown in FIGURE 1 the Wall elements are arranged alternatively with the end 13 of one element adjacent the ends 14 of the two adjacent elements. Over each cut-away end 13 of a wall element 12 is a respective metal block 15 which rests on the adjacent ends of two of the bars 11, between adjacent ends 14 of adjacent wall sections; and the blocks 15 and the ends of the bars 11 are bored to receive bolts 16 of which the heads are countersunk into the blocks 15 and by which the assembly is secured to channel-section members 17. The assembly is further secured together by tie rods 18 which pass through bores in the bars 11 and through notches 19 of the wall elements 12, and these tie rods 18 also secure L-section elements 20 against the first and last bars 11. The upper horizontal faces of the elements 20 and the upper edges of the wall elements 12 all lie in a common plane, above which the blocks 15 project slightly (say, by one sixteenth of an inch), with their upper faces also lying in a common plane. It will be seen that the bars 11, of which the upper faces also lie in a common plane, constitute the base of a serpentine channel defined by the wall elements 12 and the profiled ends of the blocks 15.

At the ends of the serpentine channel are mounted two hinge plates 21, each of these (see FIGURES 3 and 4) being bolted to one of the channel section members 17 and to a respective plate 22 welded to an end of a respective one of the elements 20 for the purpose. Each hinge plate 21 has hingedly mounted thereon a second hinge member 23, the members 23 being bolted to a channel-shaped member 17' of a second assembly (omitted from FIGURE 1 for the sake of clarity, but shown in part in FIGURES 3 and 4) complementary to that, shown in FIGURE 1, to which the hinge plates 21 are secured. In FIGURES 3 and 4, parts of the second assembly are indicated by the same reference numerals, with the addition of a superscript dash, as are used to indicate the corresponding parts of the assembly which is shown in FIGURE 1.

The two assemblies are mirror images of one another, and their hinged connection enables them to be closed to one another with the blocks 15 of the second, upper assembly resting on the blocks 15 of the lower assembly. The serpentine channel of the lower assembly, and a corresponding serpentine channel of the upper assembly, then together constitute a serpentine waveguide of which the wall constituted by the wall sections 12 and corresponding wall elements 12 of the upper assembly are slotted, since abutment of the blocks 15' with the blocks 15 leaves the wall elements 12 spaced, at their free lower edges, from the upper free edges of the wall elements 12 which are vertically below.

The hinge plates 21 are formed with apertures 24 for connection of the ends of the serpentine waveguide to a microwave source such as a magnetron and, respectively to an energy-absorbing termination such as a water load.

Suitably, the blocks 15, 15 are of height 1.42 inches, so that the height of the serpentine waveguide defined by their abutment is 2.84 inches, the height of standard waveguide size WGIO. The width of WGIO size is 1.34 inches, but as explained in Specification No. 1,050,493 above referred to the width of the serpentine waveguide may be less than this, and conveniently, it may be 0.50 inch, the bars 11 and 11' being of half-inch-square section.

If the microwave source is to be a magnetron having a WG size output, it may be matched to one of the apertures 24 by means of a tapered transition of known kind or by a quarter-wave step transformer 25, one end of which is shown in FIGURE 4 bolted to the respective hinge plate 21 using threaded holes 26 provided therein as shown in FIGURE 3. If a quarter-wave step transformer is used, it may conveniently be as shown in FIG- URE 5. As there shown, the transformer 25 is adapted at its one end to be secured to a magnetron output having a transverse internal dimension x of 1.34 inches and to present thereat a first step 27, and to be secured at its other end to the hinge plate 21 (of which the aperture 24 has a transverse dimension 2 of 0.50 inch), the hinge plate 21 presenting a second step and the transformer 25 itself having a transverse dimension of y where y =x.z. The length of the transformer, having y as its transverse dimension, i.e. the distance from a step 27 of the step transformer to a second step constituted by the part of the hinge plate 21 forming one edge of the aperture 24, is one quarter-wavelength for the microwave frequency to be employed, which may be 2450 hc./s. If a water load is secured to the other hinge plate 21, it may be similar, as shown in FIGURE 6, the end with x as its transverse dimension being in this case closed off, however, and being fitted with a tube 28, of dielectric material, for passage of water therethrough. Preferably, also, it is provided with a matching stub 29, shown only diagrammatically, of which the position is adjustable to enable the water load to be properly matched to the serpentine waveguide.

As shown in FIGURES l and 4, the bars 11 and 11' are bored with holes 30 and 30 for ventilation, to enable moisture or solvents evaporated from sheet material being heated as it passes through the slotted serpentine waveguide to be scavenged out of the waveguide. Conveniently, the upper and lower assemblies are each provided with one or more air inlet manifolds 31, each in the form of a cover or open-sided box extending, as shown in FIGURE 7, between the members 17 or 17' and in the same direction, across all the bars 11 and covering a plurality of the holes 30 or 30' of each bar. The or each inlet manifold 31 is connected by a flexible hose 32 to a supply of air (not shown) which is thus guided to the holes 30 and 30' which are covered and enters the serpentine waveguide therethrough, escaping from the waveguide through the holes 30 and 30' which are not so covered (or which, as shown in FIGURE 7, are covered by one or more exhaust manifolds 33 which may be of similar construction and each provided with a flexible exhaust hose 34). Advantageously, heating means such as infra-red heating elements are provided inside the air inlet manifolds 31 to preheat the air therein so that on passing through the holes 30 or 30 will not chill vapour which is already there at an elevated temperature. Preferably, also, the holes 30 and 30' supplied from the air inlet manifolds are fitted with nozzles, of a kind known in the printing art for similar purposes, from which the air issuing into the waveguide device emerges in a thin curtain at fairly high speed, to impinge (at an oblique angle, if desired) on a sheet of material being passed through the device and be effective as an air knife to disperse any vapour whichtends to cling to the sheet material in a thin layer immediately adjacent its surface.

It will be appreciated that the bars 11 and 11' may be replaced by hollow tubular members of rectangular cross-section, in which case the holes 30 and 30' need only penetrate to the hollow interiors, these latter serving as ducts for entry of air supplied to the ends of some of the tubular members and escape of the exhaust air from ends of the other tubular members. In that case, means is preferably provided for preheating the air supplied to those of the tubular members which serve as air inlet ducts.

The profiled ends of the members 16 and 16', which are preferably diecastings, are at least approximately semi-cylindrical; and preferably, after assembly, the narrow tapering extremities of the blocks are deformed slightly, being pressed slightly outwardly to engage tightly the adjacent wall elements 12.

It will be appreciated that it would be dangerous to open a waveguide device of the kind described above while microwave energy was being supplied to it; and the upper and lower parts of the device would therefore in practice be provided with fastening means for securing the upper part in its lowered position, the fastening means preferably incorporating switch means which would be included in the circuitry of the source of microwave energy in such manner as to prevent the supply of energy to the waveguide device at any time when the fastening means was not secured.

What we claim is:

1. A microwave heating device comprising two complementary parts which together constitute a serpentine waveguide, said parts being separable for opening the waveguide and each said part comprising a plurality of rectangular section elongate members disposed parallel with one another and each having an electrically conductive operative face disposed in a first common plane with the operative faces of the others, a plurality of electrically conductive wall elements interleaved between said elongated members alternately therewith and each in electrically conductive connection with and extending proud of the immediately adjacent ones of said operative faces and having a free edge disposed in a second common plane with the free edges of the others of said wall elements, means securing said elongate members and said wall elements together to clamp said wall elements releasably between said elongate members, and a plurality of electrically conductive end pieces each secured against end portions of said operative faces of two mutually adjacent elongate members, each wall element having one end extending between two mutually adjacent end pieces and in electrical condition therewith and another end which, between the said first plane and the said second plane, is spaced, in the longitudinal direction of the wall element, from another of said end pieces which is secured against end portions of those two elongate members between which the respective wall element is interleaved, said elongate members, wall elements and end pieces being rigidly secured together and constituting a serpentine U-section channel.

2. A microwave heating device comprising two complementary parts which together constitute a serpentine waveguide, each said part comprising a plurality of rectangular section elongate members disposed parallel with one another and each having an electrically conductive operative face disposed in a first common plane with the operative faces of the others, a plurality of electrically conductive wall elements interleaved between said elongate members alternately therewith and each in electrically conductive connection with the extending proud of the immediately adjacent ones of said operative faces and having a free edge disposed in a second common plane with the free edges of the others of said wall elements, and a plurality of electrically conductive end pieces each secured against end portions of said perative faces of two mutually adjacent elongate members, said end pieces of each said complementary part each have a flat surface disposed in a third common plane parallel with said first and second planes, said second plane being between said first and third planes, each wall element having one end extending between two mutually adjacent end pieces and in electrical connection therewith and another end which, between the said first plane and the said second plane, is spaced, in the longitudinal direction of the wall element, from another of said end pieces which is secured against end portions of those two elongate members between which the respective 'wall element is interleaved, said elongate members, wall elements and end pieces being rigidly secured together and constituting a serpentine U-section channel.

3. A device as claimed in claim 1, wherein said two complementary parts are hingedly secured together and are relatively movable between an open position and a closed position in which the said flat surfaces of the end pieces of one of said complementary parts lie on and in register with said fiat surfaces of the end pieces of the other of said complementary parts.

4. A device as claimed in claim 3, wherein said complementary parts are hingedly secured together by hinges each formed with an aperture for passage therethrough of microwave energy.

5. A device as claimed in claim 1, wherein at least some of said elongate members are formed with apertures in the said operative faces thereof for passage of air therethrough.

6. A device as claimed in claim 5, wherein at least some of said apertures are provided with nozzles shaped to direct air issuing therethrough.

7. A device as claimed in claim 5, wherein those elongate members formed with apertures are tubular for passage of air therethrough.

8. A device as claimed in claim 5, wherein said apertures extend completely through said elongate members and there are provided a plurality of air-passage manifolds each covering a plurality of apertures of each of a plurality of said elongate members.

9. A waveguide which comprises two complementary parts, and means for releasably securing said parts together to permit opening of said waveguide, each of said parts being composed of a plurality of electrically conductive elongate members disposed side-by-side, a plurality of electrically conductive wall elements interleaved with said elongate members, means securing said elongate members and said wall elements together to clamp said wall elements releasably between said elongate members, and electrically conductive side wall means disposed at opposite ends of said elongate members and said wall elements, said elongate members, said wall elements and said side wall means co-operating with each other to define through said waveguide a serpentine path for microwaves, and said respective wall elements of said complementary parts being spaced apart to define through the waveguide a slot for the material to be heated.

10. In a waveguide for microwave heating apparatus, comprising two complementary parts and means for releasably securing said parts together to permit opening of said waveguide, there being defined through said waveguide a serpentine path for microwaves said path having a plurality of side-by-side legs, and a slot for material to be heated, the improvement that each of said parts is composed of:

a plurality of electrically conductive elongate members disposed side-by-side;

a plurality of electrically conductive wall elements interleaved with said elongate members to define said plurality of legs of said path;

means securing said elongate members and said Wall elements together to clamp said wall elements releasably between said elongate members; and

means disposed at opposite ends of said elongate members and said wall elements to direct microwaves from each leg of said path to the next leg thereof.

References Cited UNITED STATES PATENTS 3,254,426 6/1966 Lamb et al 34155 3,286,369 11/1966 Smith 34-155 FOREIGN PATENTS 982,171 2/1965 Great Britain. 1,050,493 12/ 1966* Great Britain.

1,093,795 12/ 19 66 Great Britain.

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner US. Cl. X.R. 2l910.61 

